fix typo

src/Avalonia.Controls/Platform/Screen.cs

@@ -2,7 +2,7 @@
 {
     public class Screen
     {
-        public double PixelDenisty { get; }
+        public double PixelDensity { get; }
 
         public PixelRect Bounds { get; }
 
@@ -12,7 +12,7 @@
         
         public Screen(double pixelDensity, PixelRect bounds, PixelRect workingArea, bool primary)
         {
-            this.PixelDenisty = pixelDensity;
+            this.PixelDensity = pixelDensity;
             this.Bounds = bounds;
             this.WorkingArea = workingArea;
             this.Primary = primary;